Protective system



Nov. 4, 1941.

Hey deflection Ray deflect/on Source.

J. L. DELVAUX PROTECTIVE SYSTEM Filed Feb. 27, 1940 Fig.1.

Ray deflect/ Z7 SOLff'CE. Z9 25 Z7 8 silica.

Modulation 7 SOLlf'C.

Fig.2.

Ray deflection Source. 22 Z5 Inventor:

Jean L. Delvaux,

I Patented Nov. 4, 1941 PROTECTIVE SYSTEM Jean L. Delvaux, Paris, France, assignor to General Electric Company, a corporation of New 7 Application February 2'7, 1940, Serial No. 321,065.

In France May 11, 1939 1. Qh ms- My invention relates to protective systems for electron discharge devices, and more particularly to systems for the protection of devices of the cathode-ray type. p

In the operation of an electron discharge device of the cathode-ray type, a-more or less concentrated electron beam is directed against a sensitivevsurface comprising ascreen, mosaic, fluorescent coating, or the like. Through the action of suitable scanning or ray-deflecting circuits the beam is caused to traverse the sensitive, surface periodically. Such devices have wide application, for example in oscilloscopes, oscillographs, television transmitters, and television receivers.

In the event of any failure of the-scanning or ray-deflecting circuits to operate properly, damage to the sensitive surface may result from the action of the concentrated electron beam upon a limited area of the surface foreven a very short time. Therefore, it is highly desirable to pro,-

' vide means for removing the beam from the surfaceimmediately in response to conditionscause ing such a failure. I

Various means toaccomplish this result have been proposed. For example, one such protece tive system heretofore employed comprises one or more thermionic devices with associated input and output circuits. Potentials derived from the ray-deflecting circuits and applied to the input circuits control the flow of current through the 1 actuating coil, or coils, of one or more electromagnetic relays included in the output circuits. The relay,'or relays, in turn control the energization and deenergization of a power supply trans.-

1 former which provides the operating potentials for the cathode-ray tube to be protected. Thus, afailur in a scanning circuit causes deenergization of the power supply circuit. Such a system as this has several disadvantages, the mostserious being complete loss of protection for the cathode.- ray tube if the mechanical relay, or relays, should stick or otherwise become inoperative.

It is, accordingly, anobject of my invention to provide improved protective means for electron discharge devices, particularly for devices of the cathode-ray type.

It is a further object of my invention to pro vide a simple, economical and effective protective system in which no mechanical devices are employed, the protection being provided purely by electrical means.

The features of my invention which I believe to be novel are set forth with particularity in the appended cl ims. My in n io i s l ow er may be a source of video signals.

tion, together with furtherrob jects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 diagrammatically illustrates one embodiment of my invention, and Fig. 2 is a fragmentary diagrammatic representation of a modification of a portion of the circuit of Fig. 1.

In both figures corresponding elements have been indicated by corresponding reference nuals Referring now to Fig. 1, an electron discharge device'l is illustrated in this particular embodiment as being a cathode-ray tube of conventional design. The discharge device illustrated is particularly adapted for television receiver circuits, though it will be understood that it may take various forms. As shown the device I comprises a cathode 2, a control grid 3 and a main anode 4. There may of course be other electrodes, but the presence or absence of these has no bearing on the present invention. Electrons emitted by the cathode 2 are directed in a more or less concentrated stream against the end of the tube envelope, the inner surface of which is provided with a fluorescent screen or coating 5.

Potentials are impressed upon the grid 3 through a conductor I from a modulation source 6, which in a television receiver, for example,

A positive potential is impressed upon the anode 4 by the direct The potentiometer I2 provides a means for varying the average potential of the grid 3 with respect to the cathode 2, which in a television receiver permits adjustment of the average brightness of the image formed on the surface 5 as is well known in the art.

The thermionic devices I6 and I! are illustrated as diodes having directly heated cathodes 8. nd I9 and no e 20 and 2 es c ive y. These diodes are connected in series between the cathode 2 and the conductor I5; The centertapped resistors 22 and 23 provide means for makboth a wi s or an a on and. method 9f QB???" ing "connection to eagh cathode circuit at a Point of average cathode potential, in the conventional manner.

On either side of the discharge device I are shown ray-deflection sources 24 and 25. Potentials supplied from these sources through two pairs of deflecting coils 26 and 21 respectively cause the electron beam to traverse the surface 5 according to a predetermined pattern in a Wellknown manner. For example, in a television receiver these sources may provide the vertical and horizontal scanning potentials. While the deflecting means have been illustrated as of the electromagnetic type, it will of course be understood that they may be of the electrostatic type or a combination of the two types.

Between the pairs of coils 25 and 21 are connected resistors 28 and 29 respectively. The resistor 28 is connected in circuit with the cathode 19 through the conductors 30 and the resistor 29 is similarly connected in circuit with the cathode l8 through the conductors 3|. Thus, flow of current in either ray-deflecting circuit causes a potential to be developed across the resistor included therein, in turn providing a flow of heating current through the cathode connected in circuit with that resistor.

Since the resistor 22 is in parallel with the resistor 29, it will be obvious that these resistors may be combined. The same is also true of the resistors 23 and 28.

The connection between the cathode 2 and the negative terminal of the direct current source 8 through the conductor 32 and capacitor 33 provides a by-pass for the alternating components of the anode-cathode current. A high resistance 34, preferably having a resistance of several megohms, is connected between conductors 32 and to protect the cathode against overvoltage.

The operation of this system is as follows:If the ray deflection sources 24 and 25 are energized to cause the ray-deflecting potentials to be applied to the pairs of coils 25 and 21, current will flow through the resistors 28 and 29. Thus, the cathodes of the diodes l6 and I! will be energized and the diodes rendered in a conducting state. This permits the application of anode potential to the device I, which then operates in the usual manner. Now if for any reason one of the ray-deflection devices or sources fails, the current derived therefrom for heating the corresponding diode is removed. Since the impedance of the diode immediately assumes a very high value, the anode to cathode circuit of the device I is eifectively opened, removing the electron beam from the sensitive surface.

It may be desirable to connect the cathodes of the diodes I 6 and I! to the ray-deflection sources H and I2 through transformers rather than resistors. A modification of this portion of the circuit is illustrated in Fig. 2. This corresponds in all respects to Fig. 1, excepting that the resistors 22, 23, 28 and 29 have been replaced by the filament transformers 35 and 36. The secondaries of these transformers are also provided with center taps for connections at points of average cathode potential in the usual manner.

It is desirable to render the heating currents through the cathodes I8 and I9 substantially independent of normal fluctuations in the ray-deflection potentials. To accomplish this result known regulating devices may be employed in the filament circuits; for example, non-linear resistances, or resistances with a negative characteristic. The diodes l6 and I! should also be chosen for low current consumption, low thermal inertia and low anode to cathode voltage drop.

It is obvious that many modifications may be made in the above-described circuits. There may be any number of thermionic protective devices associated with the electron discharge device to be protected, their number being determined by the number of control circuits upon whose proper functioning the safe operation of the discharge device depends. If the cathode 2 of the device I is of the directly-heated type, it may be supplied with heating current derived from a ray-deflection circuit, or other control circuit, exactly as described for the diodes l6 and IT; or if the cathode 2 is of the indirectlyheated type, the heating filament may be insulated from the cathode 2 and energized in the same manner.

While the protective devices l6 and I! have been illustrated as diodes of the directly heated type, it is obvious that they may be of the indirectly heated type, or that they may have more than two electrodes. They may be mounted within a common tube envelope or even within the envelope of the tube I itself.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since modifications may be made, both in the circuit arrangement and instrumentalities employed, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electron discharge device, a thermionic device having an anode and electrically heated cathode, connections for applying potential to said discharge device for developing an electron discharge therein, said connections including the anode to cathode path of said thermionic device, control means for directly influencing said discharge, means for energizing said control means, and means for supplying current for heating said cathode in response to energization of said control means, whereby said discharge can be developed onlv when said control means is energized.

2. In combination, an electron discharge device having an anode and a cathode, a thermionic device having an anode and an electrically heated cathode, means for developing an electron discharge in said discharge device comprising in series circuit relation a source of potential and the anode to cathode paths of said devices, control means for directly influencing said discharge, means for energizing said control means, and means for supplying heating current to said electrically heated cathode in response to energization of said control means, whereby said discharge can be developed only when said control means is energized.

3. In combination, an electron discharge device of the cathode ray type, a thermionic device having an anode and an electrically heated cathode, connections for applying potential to said discharge device for developing a cathode ray therein, said connections including the anode to cathode path of said thermionic device, means for deflecting said cathode ray, means for energizing said ray deflecting means, and means for supplying current for heating said cathode in response to energization of said flecting saidcathode ray, means for energizing said ray-deflecting means, and means for supplying heating current to said electrically heated cathode in response to energization of i I said ray-deflecting means,whereby said cathode ray can be developed only when said ray deflecting means is energized.

5. In combination, a cathode ray device having means to develop a cathode ray discharge therein,

' 1 a thermionic device having an electrically heated cathode, a source of unidirectional potential, circuit connections including in series circuit relation said devices and said source, means for deflecting said ray discharge, and means for deriving current for heating said cathode from said ray deflecting means.

6. In a protective system, a cathode ray discharge device having a sensitive surface therein to be protected, means within said device for producing a cathode ray and an anode for accelerating said ray toward said surface, a thermionic device having an electrically, heated cathode, means for applying a positive potential to said anode through the space discharge path of said thermionic device, meansfor deflecting said ray,

and means for deriving current for heating said cathode from said ray deflecting means, whereby the thermionic device is rendered non-conducting upon failure of said ray deflecting means and application of anode potential to said discharge device thereby prevented.

'7. In a protective system, the combination with a cathode ray discharge device having a sensitive surface therein to be protected, a cathode within said device for producing a cath 'ode ray and an anode 'for accelerating said ray response to energization of said ray deflectingmeans, whereby said thermionic device is rendered non-conducting and said discharge device inoperative upon deenergization of said ray deflecting means.

8. In a protective system, the combination with a cathode ray discharge device having an electron emissive cathode, an anode and a sensitive surface to be protected, of a thermionic device having an anode and a filamentary cathode,

" a source of unidirectional potential, connections for impressing said potential between the anode and cathode of said discharge device for developing a cathode ray discharge therein, said connections including the anode to cathode path of said thermionic device, means for deflecting said cathode ray comprising a deflecting coil, a fluctuating source of potential for energizing said ray deflecting means, and means for supplying heating current to said filamentary cathode in response to energization of said ray deflecting means, whereby said thermionic device is rendered non-conducting and said discharge device inoperative upon deenergization of said ray deflecting means.

9. In combination, a cathode ray discharge device having an electron emissive cathode, an anode and a sensitive surface, a thermionic device having an anode and a filamentary cathode, a

source of unidirectional potential, connections for impressing said potential between the anode and cathode of said discharge device for developing a cathode ray discharge therein, said connections including the anode to cathode path of said thermionic device, means for deflecting said cathode ray comprising a deflecting coil, a source of deflecting potentials, and an impedance connected in series, and means for connecting the filamentary cathode of said thermionic device across said impedance for supplying heating current thereto from said deflecting source, whereby said thermionic device is rendered non-conducting upon failure of said deflecting coil or said deflecting source and application of potential to 7 said discharge device is thereby prevented.

10. In combination, a cathode ray discharge device having an electron emissive cathode, an anode and a sensitive surface, a plurality of thermionic devices each having an anode and an electrically heated cathode, connections forimpressing a potential between the anode and cathode of said discharge device to produce a cathode ray discharge therein, said connections including the anode to cathode paths of all said thermionic devices in series, a plurality of means for deflecting said discharge, and means for deriving the cathode heating current for each of said thermionic devices from a different one of said deflecting means.

11. In a protective system, the combination with a cathode ray discharge device having an electron emissive cathode, an anode and a sensitive surface to be protected, of a plurality of thermionic devices each having an anode and a filamentary cathode, a source of unidirectional potential, connections for impressing said potential between the anode and cathode ofsaid discharge device to produce a cathode ray discharge therein, said connections including the anode to cathode paths of all said thermionic devices in series, a plurality of ray deflecting means for deflecting said discharge, and means for supplying heating current to the filamentary cathode of each thermionic device in response to the energization of a different one of said ray deflecting means, whereby each thermionic device is rendered non-conducting upon deenergization of the corresponding ray deflecting means and whereby said discharge device is rendered inoperative upon deenergization of any one of said ray deflecting means. JEAN L. DELVAUX. 

